The present invention relates to power electronics equipment. Specifically, the present invention relates to power electronics equipment well suited for transmitting signals to switching devices via insulating transformers.
Vehicle equipment is mounted with a step-up and step-down converter and an inverter on the driving system of a motor that generates driving power for improving conversion efficiency and for reducing energy consumption.
FIG. 11 is a block diagram schematically showing a vehicle driving system that employs a conventional step-up and step-down converter.
Referring now to FIG. 11, the vehicle driving system includes a power supply 1101 that feeds electric power to a step-up and step-down converter 1102 that boosts and steps down a voltage, an inverter 1103 that converts the voltage outputted from step-up and step-down converter 1102 to the components of a three-phase voltage, and a motor 1104 that drives the vehicle. Power supply 1101 may be comprised of a voltage fed through overhead wires or batteries connected in series.
In driving the vehicle, step-up and step-down converter 1102 boosts the voltage of power supply 1101 (e.g. 280 V) to a voltage suited for driving motor 1104 (e.g. 750 V) and feeds the boosted voltage to inverter 1103. By controlling the ON and OFF state of the switching devices in inverter 1103, the voltage boosted by step-up and step-down converter 1102 is applied during each phase of motor 1104 and a phase shift and current flow is generated. By controlling the switching frequency of inverter 1103, the vehicle speed can be changed.
In braking the vehicle, inverter 1103 controls the ON and OFF state of the switching devices synchronizing with voltage components generated in the phases of motor 1104 to rectify and convert the three-phase voltage to a DC voltage that feeds step-up and step-down converter 1102. Step-up and step-down converter 1102 steps down the voltage generated in motor 1104 (e.g. 750 V) to the voltage of power supply 1101 (e.g. 280 V) to conduct regeneration operations.
FIG. 12 is a block circuit diagram of the step-up and step-down converter shown in FIG. 11.
Referring now to FIG. 12, step-up and step-down converter 1102 includes a reactor L for energy storage, capacitor C that accumulates electric charges, switching devices SW1 and SW2 that directs current flow into inverter 1103 and interrupt the current flowing into inverter 1103. Converter 1102 also includes and control circuits 1111 and 1112 that generate control signals directing the conduction and non-conduction of switching devices SW1 and SW2.
Switching devices SW1 and SW2 are connected in series. Power supply 1101 is connected to the connection point of switching devices SW1 and SW2 via reactor L. Switching device SW1 comprises an insulated gate bipolar transistor (hereinafter referred to as an “IGBT”) 1105 that conducts switching operations in response to the control signal from control circuit 1111. A free-wheel diode D1 is connected in parallel to IGBT 1105 and makes a current flow in a direction opposite to the direction of the current flowing through IGBT 1105.
Switching device SW2 comprises an IGBT 1106 that conducts switching operations in response to the control signal from control circuit 1112. A free-wheel diode D2 is connected in parallel to IGBT 1106 and makes a current flow in a direction opposite to the flow direction of the current flowing through IGBT 1106. The collector of IGBT 1106 is connected to capacitor C and inverter 1103.
FIG. 13 is a wave chart illustrating the waveform of the current flowing through reactor L, shown in FIG. 12, in the boosting operation.
Referring now to FIG. 13, as IGBT 1105 in switching device SW1 becomes ON (conductive) in the boosting operation, a current I flows through reactor L via IGBT 1105, storing the energy of LI2/2 in reactor L.
Then, as IGBT 1105 in switching device SW1 becomes OFF (nonconductive), a current flows through free-wheel diode D2 in switching device SW2, transferring the energy stored in reactor L to capacitor C.
In the stepping down operation, as IGBT 1106 in switching device SW2 becomes ON (conductive), a current I flows through reactor L via IGBT 1106, storing the energy of LI2/2 in reactor L.
Then, as IGBT 1106 in switching device SW2 becomes OFF (nonconductive), a current flows through free-wheel diode D1 in switching device SW1, regenerating the energy stored in reactor L to power supply 1101.
By changing the ON-period (ON duty) of the switching devices, the boosted and stepped down voltages maybe adjusted. The approximate voltage value is obtained from the following formula.VL/VH=ON duty (%)
Here, VL is the power supply voltage, VH is the voltage after the boosting or the stepping down, and the ON duty is the ratio of the conduction period of switching device SW1 or SW2 to the switching period thereof.
In practice, there are variations in the load and the power supply voltage VL. Therefore, the ON period (ON duty) of switching device SW1 or SW2 is controlled by means of monitoring the voltage VH after the boosting or the stepping down so that after the boosting or the stepping down, the voltage VH may be made equal to the reference value.
Since control circuits 1111 and 1112, grounded to the vehicle body, are on the low voltage side, the arms connected to switching devices SW1 and SW2 are on the high voltage side. So as not to expose any human body to danger, even if an accident, such as the breakdown of switching device SW1 or SW2 is caused, signal transmission and reception are conducted between the arms and control circuits 1111, 1112, while the arms and control circuits 1111, 1112 are electrically insulated from each other by photocouplers.
FIG. 14 is a block diagram schematically showing an intelligent power module for the conventional step-up and step-down converter.
Referring now to FIG. 14, the intelligent power module for the step-up and step-down converter includes switching devices SWU and SWD that direct current flow to the load and interrupt the current flowing to the load. The intelligent power module also includes a control circuit 1 that generates control signals directing the conduction and non-conduction of switching devices SWU and SWD. Control circuit 1 may be comprised of a CPU 4 or a logic IC, or a system LSI that mounts a logic IC and a CPU thereon.
Switching devices SWU and SWD are connected in series so that SWU and SWD may work for an upper arm 2 and for a lower arm 3, respectively. The SWU includes an IGBT 6 that conducts switching operations in response to a gate signal SU4. A free-wheel diode DU1 that makes a current flow in a direction opposite to the flow of current through IGBT 6 is connected in parallel to IGBT 6. The chip on which IGBT 6 is formed includes a temperature sensor that uses the VF (Forward Voltage) change of a diode DU2, caused by the chip temperature change, to measure temperature. In addition, a current sensor, which detects the main circuit current by dividing the emitter current of IGBT 6 with resistors RU1 and RU2, is included in the chip.
An IGBT 5 that conducts switching operations in response to a gate signal SD4 is disposed in switching device SWD. A free-wheel diode DD1 that makes a current flow in a direction opposite to the current flowing through IGBT 5 is connected in parallel to IGBT 5. On the chip, in which IGBT 5 is formed, a temperature sensor, which employs the VF change of a diode DD2 caused by the chip temperature change for the measurement principle thereof, and a current sensor, which detects the main circuit current by dividing the emitter current of IGBT 5 with resistors RD1 and RD2, are disposed.
On the side of upper arm 2, a gate driver IC 8 provides protection functions that monitors an overheat detection signal SU6 from the temperature sensor and an overcurrent detection signal SU5 from the current sensor and further generates a gate signal SU4 for driving the control terminal of IGBT 6. An analog-PWM converter CU that generates a PWM signal indicating the temperature of IGBT 6 is also disposed on the side of upper arm 2.
On the side of lower arm 3, a gate driver IC 7 provides protection functions that monitors an overheat detection signal SD6 from the temperature sensor and an overcurrent detection signal SD5 from the current sensor and generates a gate signal SD4 for driving the control terminal of IGBT 5. Also disposed on the side of lower arm 3 is an analog-PWM converter CD that generates a PWM signal corresponding to the temperature of IGBT 5.
Photocouplers FU1 through FU3 are inserted between control circuit 1, grounded to the vehicle body and upper arm 2, biased at a high voltage. Photocouplers FD1 through FD3 are inserted between control circuit 1, grounded to the vehicle body, and lower arm 3, biased at a high voltage. Control circuit 1 transmits signals to upper arm 2 and receives signals from upper arm 2 via photocouplers FU1 through FU3, while control circuit 1 is insulated electrically from upper arm 2 by photocouplers FU1 through FU3. Control circuit 1 transmits signals to lower arm 3 and receives signals from lower arm 3 via photocouplers FD1 through FD3, while control circuit 1 is insulated electrically from lower arm 3 by photocouplers FD1 through FD3.
In detail, a PWM (Pulse Width Modulation) gate driving signal SU1 is output from CPU 4 and is inputted to gate driver IC 8, which provides protection functions, in upper arm 2 via photocoupler FU1. An alarm signal SU2 outputted from gate driver IC 8 which provides protection functions, is inputted to CPU 4 via photocoupler FU2. A PWM signal SU3 indicating the IGBT chip temperature and outputted from analog-PWM converter CU is inputted to CPU 4 via photocoupler FU3.
A PWM gate driving signal SD1 is outputted from CPU 4 and is inputted to gate driver IC 7, which provides protection functions, in the lower arm 3 via photocoupler FD1. An alarm signal SD2 outputted from gate driver IC 7, which provides protection functions, is inputted to CPU 4 via photocoupler FD2. A PWM signal SD3 indicating the IGBT chip temperature and outputted from analog-PWM converter CD is inputted to CPU 4 via photocoupler FD3.
FIG. 15 is a block diagram schematically showing the peripheral circuit of a photocoupler.
Referring now to FIG. 15, photocoupler 2008 includes: an infrared light emitting diode 2003 that emits an infrared ray based on a forward current If, a light receiving diode 2004 that receives the emitted infrared ray, and a bipolar transistor 2005 that conducts current amplifying operations employing the photocurrent generated in light receiving diode 2004 for the base current thereof. The cathode of infrared light emitting diode 2003 is connected to a field effect transistor 2001 via a resistor 2002. The collector of bipolar transistor 2005 is connected to a power supply voltage Vcc2 via a resistor 2006. An output signal Vout, outputted via the collector of bipolar transistor 2005, is inputted to an IGBT driver IC 2007.
As a signal SP is inputted to the gate of field effect transistor 2001, forward current If flows through infrared light emitting diode 2003, emitting an infrared ray. The infrared ray emitted from infrared light emitting diode 2003 is received by light receiving diode 2004 and a photocurrent corresponding to the received infrared ray flows to the base of bipolar transistor 2005. As the photocurrent flows to the base of bipolar transistor 2005, a collector current IC flows to bipolar transistor 2005. By making collector current IC flow through resistor 2006, the first end of which is connected to the power supply voltage Vcc2, the voltage change at the second end of resistor 2006 is inputted to IGBT driver IC 2007 as output signal Vout.
The input and output characteristics of photocoupler 2008 are defined by the current transfer ratio (hereinafter referred to as the “CTR”), that is, IC/If. In designing a circuit using photocoupler 2008, it is necessary to consider (1) the temperature characteristics of the current amplification factor hfe of bipolar transistor 2005, (2) the deterioration by aging of the light emission efficiency of infrared light emitting diode 2003, (3) the variations of the CTR, and such factors.
FIG. 16 is a curve describing the temperature dependence of the current transfer ratio of the photocoupler.
Referring now to FIG. 16, the current transfer ratio of photocoupler 2008 is lower, as the temperature is lower due to the temperature dependence of the current amplification factor hfe of bipolar transistor 2005.
FIG. 17 is a curve depicting the deterioration by aging of the current transfer ratio of the photocoupler, and illustrates whereby the CTR of photocoupler 2008 decreases depending on the forward current, environmental temperature and accumulated operating time of light emitting diode 2003. Especially when photocoupler 2008 is used continuously for more than 1000 hr, remarkable CTR lowering is caused.
Alternatively to the photocoupler, an insulating transformer is used for a means for insulating the transmitted signal.
FIG. 18 is a top plan view schematically showing a conventional insulating transformer for signal transmission.
Referring now to FIG. 18, the insulating transformer includes a magnetic core MC. A primary winding M1 and a secondary winding M2 are wound around magnetic core MC. Magnetic core MC may be made of ferrite, permalloy and other such ferromagnetic material. The magnetic flux φ generated by the current fed to primary winding M1 is localized into magnetic core MC and is made to pass through magnetic core MC. Magnetic flux φ intersects secondary winding M2, generating a voltage dφ/dT across secondary winding M2. Since a closed magnetic path is formed by using magnetic core MC, the adverse effects of the external magnetic field are reduced and the coupling coefficient of primary winding M1 and secondary winding M2 is increased.
FIG. 19 is a block diagram of a signal transmission circuit using a conventional insulating transformer for signal transmission.
Referring now to FIG. 19, a first end of the primary winding in an insulating transformer T is connected to the drain of a field effect transistor M1 via a resistor R1, and a first end of the secondary winding in insulating transformer T is connected to a demodulator circuit 1203. A local oscillation signal generated in a local oscillator circuit 1201 is inputted to a modulator circuit 1202. As a PWM signal SP is inputted to modulator circuit 1202, the local oscillation signal is modulated by PWM signal SP and the modulated local oscillation signal is inputted to the gate of field effect transistor M1 for the control signal thereof. As the control signal is inputted to the gate of field effect transistor M1, a modulated signal modulated at a high frequency is inputted to demodulator circuit 1203 via insulating transformer T, and PWM signal SP is demodulated in demodulator circuit 1203.
The following Patent Document 1 discloses an induction heating apparatus including a heating roller, which includes a hollow roller base body and a plurality of secondary coils formed over the roller base body, and a primary coil disposed in the heating roller, wherein the primary and secondary coils are coupled with each other in an induction transformer coupling relationship to improve the electric power transfer efficiency thereof.
The following Patent Document 2 discloses the connection of a driver formed on a first substrate and a receiver formed on a second substrate by the magnetic coupling using coils.
The following Patent Document 3 discloses the use of a link coupling transformer as a logic separation circuit for isolating an input circuit and an output circuit from each other.
[Patent Document 1] Japanese Patent Application Publication No. 2002-222688 (Counterpart U.S. Pat. No. 6,847,019)
[Patent Document 2] Published Japanese Translation of PCT International Publication for Patent Application 2001-521160 (Counterpart U.S. Pat. No. 6,054,780)
[Patent Document 3] Published Japanese Translation of PCT International Publication for Patent Application 2001-513276 (Counterpart U.S. Pat. No. 5,952,849)
However, because it is necessary, for the method that employs photocouplers as the means for insulating the transmitted signals, to consider (1) the temperature characteristics of the current amplification factor hfe of a transistor, (2) the deterioration by aging of the light emission efficiency of a light emitting diode, and (3) the variations of the CTR, it is difficult to design a circuit that can be used continuously over 10 years in vehicles, industrial equipments and such high temperature environments.
The use of a cored transformer as an insulating transformer for signal transmission is affected adversely by the temperature dependence of the magnetic permeability of a magnetic core material, the high temperature dependence of the coupling coefficient, and the difficulties in reducing the costs and dimensions of the apparatus. Since it is impossible to directly send the PWM signal via the cored transformer, it is necessary to modulate the PWM signal at a high frequency and to demodulate the modulated signal received by the secondary winding. Therefore, the circuit scale is inevitably large.
Since the use of an air-cored transformer as an insulating transformer for signal transmission does not employ any magnetic core, the use of the air-cored transformer facilitates reducing the costs and dimensions of the apparatus. However, since the magnetic circuit is not closed, external magnetic fluxes are liable to be superimposed as noise onto the secondary winding, causing malfunctions.
In view of the foregoing, it would be desirable to provide power electronics equipment that facilitates suppressing the deterioration by aging, improving the resistance against hazardous environments, reducing the adverse effects of noises caused by external magnetic fluxes, and transmitting and receiving signals between the high and low voltage sides, while insulating the high and low voltage sides electrically from each other.
Further objects and advantages of the invention will be apparent from the following description of the invention.